Once upon a time Gandharvas of collective name Mauneya defeated the Nagas and snatched all their wealth and powers. The Nagas prayed Lord Vishnu to rescue them. Lord Vishnu told them that he would appear in Mandhata’s son Purukutsa and kill the Gandharvas. Afterwards Narmada brought Purukutsa to Rasatal where Lord Vishnu appeared in his body. Thus having the strength of Lord Vishnu, Purukutsa defeated and killed the Gandharvas. Pleased by the action of Narmada, the Nagas blessed her with a boon that whoever remembered her would have no fear of snake venom and Purukutsa that he would have an immortal son.
Purukutsa and Narmada had a son Trasadasyu. Lineage of Trasadasyu continued as follows- Trasadasyu, Anaranya, Vrihadashva, Haryashva, Hasta, Sumana, Tridhanva, Trayaruni and Satyavrat. Satyavrat became famous as Trishanku in later course. By the curse of a sage, Trishanku had become a Chandala. Once a drought occurred for twelve long years. During that drought, to get rid from this condition of Chandala and feed sage Vishwamitra, Trishanku used to tie a whole skinned deer to a Banyan tree on the bank of the river Ganges. Pleased by his selfless service, sage Vishwamitra sent Trishanku to the heaven with his ephemeral body.
Lineage of Trishanku grew as follows- Trishanku, Harishchandra, Rohitashva, Harit, Chanchu, Vijay, and Vasudev. Vijay had a son Ruruk. Ruruk’s son was Vrik who had a son Bahu. Bahu had two queens. After a long time of their marriage, Bahu’s queen consort conceived a son. But the circumstances took a strange turn. Bahu’s enemies together attacked his kingdom and defeated him. The defeated king migrated to the forest along with his queens and began to live at the hermitage of sage Aurv. Very soon, King Bahu died of old age. His queen consort also wanted to commit Sati but sage Aurv prevented her from doing so. After sometime getting envious of her fortune, the other queen deceitfully fed her with poison. But the poison could not harm the foetus, which stayed unborn for a period of seven years because of poison’s effect.
Staying at the hermitage of sage Aurv, the queen consort gave birth to a son. Since the child was born with the effect of the poison, Sage Aurv named him as Sagar. Sagar began to grow in he hermitage in natural surrounding. One day he asked his mother about his father. The queen narrated the whole incident to him. Sagar then and there took an oath to exterminate the Kshatriyas who had been the cause of his father’s death. Acting as per his oath, Sagar destroyed Haihaya Kshatriyas whereas Shak Kshatriyas got their heads shaven out of fear. Since those Kshatriyas had given up their religion, hence Brahmins boycotted them. As a result they became Malechchha. Thereafter King Sagar returned to his capital and ruled the earth.